Cardiovascular disease (CVD) is one of the leading causes of morbidity and mortality in the United States. There is evidence that premenopausal women are much less prone to suffer CVD than males of similar age, and that this advantage disappears after menopause. Using a mouse model of myocardial infarction (MI), we recently found that female mice had a much lower cardiac rupture rate and better preserved left ventricular (LV) function than males after MI. Supplementation of estrogen and/or castration in males reduced the rupture rate and slowed LV remodeling, while supplementation of testosterone in females increased the incidence of rupture and worsened cardiac function and remodeling, indicating a protective role of estrogen and detrimental role of testosterone post-MI. In this proposal, we will further test the hypotheses that estrogen, acting on the alpha-receptors, protects the heart from early (infarct expansion and cardiacrupture) and late remodeling (cardiac hypertrophy, dilatation and dysfunction) and this effect is partially mediated by facilitating the healing process during acute MI, and by inhibiting the inflammatory response and reducing oxidative stress during the development of heart failure. Conversely, testosterone exacerbates the inflammatory response. In Aim 1, we will study the effect of estrogen and testosterone on infarct healing, including inflammatory cell infiltration, collagenase activity, collagen deposition, infarct expansion and neovascularization. In Aim 2, we will study whether, during the chronic phase of MI, estrogen decreases nuclear factor-kappaB and reactive oxygen species, thereby ameliorating the inflammatory response and improving cardiac function in males, whereas testosterone aggravates inflammation and cardiac dysfunction. In Aim 3, we will study whether the cardioprotective effect of estrogen is mediated by activation of its alpha-receptor. In Aim 4, we will study whether 1) estrogen given soon after ovariectomy (mimics early postmenopausal status) will provide better cardiac protection than if it is given a few weeks later (mimics late postmenopausal status) when mice are subjected to MI;and 2) the cardioprotective effect of estrogen will be attenuated when combined with progestin.